Underground storage vessels are commonly used for the storage of a variety of fluids including water, chemicals and hydrocarbons. In the past, such vessels have been typically comprised of steel. However, steel vessels are relatively heavy, leading to difficulties with the transportation and installation of such vessels and the resulting costs associated with such difficulties. Further, steel vessels are subject to corrosion when left in place for a substantial period of time. As a result of the tendency to corrode over the years, regular repair and replacement of these vessels is often required in order to avoid vessel failure and the resulting potential for ground contamination when the vessel contains environmentally hazardous fluids.
As a result of the difficulties associated with underground storage vessels made of steel, many underground storage vessels in use today are comprised of fiberglass. These fiberglass storage vessels may be single walled or double walled where secondary containment is desired for hazardous fluids contained within the vessel. For instance, the majority of underground fiberglass vessels are double walled with a monitor in the interstitial space between the inner and outer walls in order to ensure the integrity of the walls. It has been found that fiberglass is relatively light in weight as compared to steel and that it is corrosion free both internally and externally. Accordingly, fiberglass tends to be well suited for underground installation.
However, fiberglass vessels often present their own difficulties with respect to their use and installation. For instance, fiberglass vessels are relatively delicate in that the material tends to be easily damaged. Where the fiberglass material is damaged, there is a risk of vessel failure, with the resulting environmental hazards and remediation costs, including the cost of replacement or repair of the vessel. More particularly, fiberglass vessels are commonly subjected to material damage during handling and loading of the vessel both prior to and during installation at a new site. Similarly, damage may be caused during the relocation or removal of a vessel from an existing site.
Further, the vessel wall may fail as a result of stresses or forces imposed on the installed vessel due to ground movement or settling of the vessel or due to the effects of buoyancy on the vessel from any ground water at the site. Ground movement or settling, the effects of buoyancy and improper installation may also lead to a failure of the nozzles or fittings associated with the vessel at the point or location of connection of the fittings to the vessel. Finally, current methods for the installation of underground storage vessels, and in particular fiberglass vessels, as discussed further below, tend to be both relatively costly, time consuming and potentially hazardous.
One method of installing underground storage vessels, including fiberglass storage vessels, requires extensive site preparation including the installation of an anchoring system. Specifically, the intended site of the storage vessel is excavated to the necessary dimensions to permit the installation of the vessel and to permit one or more people to work within the excavation. An anchoring system is then installed at the base of the excavation. A typical anchoring system includes concrete holddowns or pile holddowns installed at the base of the site and one or more straps which pass about the vessel and are connected to the holddowns. The vessel is lowered into the site and the anchoring system is manually connected to the vessel. The excavated site is then backfilled to the ground surface. Further, once the installation is completed, the storage vessel is typically tested to ensure the integrity of the underground system.
As the vessel is installed directly into the excavated site, the site must be carefully prepared and compacted, where necessary, prior to the installation of the storage vessel. In addition, the anchoring system must be installed within the site prior to the installation of the vessel. Further, if excessive water accumulation is anticipated at the excavated site or the site has a particularly high water table, the water level must be kept as low as possible during installation in order to properly install the vessel. As a result, the use of pumps and ballast tanks may be required for the installation. Finally, the installation of the anchoring system is critical to the reliability or integrity of the vessel. Specifically, small shifts in the position of the anchoring system may lead to shifts in the position of the storage vessel, which may lead to a rupture or failure of the fittings or piping between the vessel and the surface. Typically, such failures occur at the point or location of the connection of the fitting to the vessel.
Once the site is prepared, the vessel is shipped to the site and installed in a relatively unprotected state. As a result, significant damage may occur to the material of the vessel during the shipping and installation procedures. Similarly, in the event that repair of the storage vessel is required, excavation of the unprotected vessel may also result in significant damage to the vessel.
As well, the installation of the anchoring system, the installation of the vessel and the connection of the anchoring system to the vessel are typically labor intensive tasks and typically require one or more people to work within the excavated site. The need for the presence of one or more people within the excavated site presents various excavation requirements in order to provide access to the site and to minimize any resulting safety hazards. For instance, strict safety standards for the excavation must typically be followed, including requirements for a relatively large excavation site and for sloping of the excavated walls. These requirements may increase the cost of the preparation of the site prior to the actual installation of the vessel.
Further, the backfill for the excavated site must be carefully selected given the direct physical contact of the backfill with the storage vessel. This is particularly important when the storage vessel is made of fiberglass. The need for a particular type of backfill may further increase the cost of the installation. As well, the backfill operation must be carefully conducted in order to avoid damage to the vessel and proper compaction about the vessel.
A further method of installing underground storage vessels is to provide an underground vault in which the storage vessel is installed. As the vessel is placed within the underground vault, some protection is provided to the vessel following the installation. As well, where environmentally hazardous fluids are contained within the vessel, the vault may provide secondary containment in the event of any leakage. However, this method of installation is also not completely satisfactory.
For instance, the site must still be prepared in advance of the installation of the vessel by either preparing or constructing the vault on-site or assembling pre-fabricated elements of the vault at the site. Alternately, the fully assembled vessel and vault structure may be transported to the site for installation, however, the size and weight of the fully assembled unit may present problems with respect to its transportation to and installation at the site. In addition, in some cases, the vault itself may require the installation of an anchoring system at the site or the attachment of deadweights to ensure the anchoring of the vault structure. Thus, this method of installation and subsequent testing of underground storage vessels continues to be time consuming, labor intensive and presents its own disadvantages and safety hazards which must be addressed.
Further, unless the vault is transported to the site within a fully assembled vault structure, the vessel must still be shipped to the site for installation in a relatively unprotected state. Thus, significant damage may still occur to the material of the vessel during the shipping and installation procedures. Similarly, although the vault provides some measure of protection to the vessel, repair or replacement of the unprotected vessel may result in damage to the vessel, particularly where the vault contains backfill material about the vessel.
One example of a vault which is prepared on-site is provided by U.S. Pat. No. 4,934,866 issued Jun. 19, 1990 to Gage. Gage describes an underground fiberglass vault into which one or more underground storage vessels are secured. To install the vault, a pit is excavated and a concrete base is poured in the bottom of the pit. The sides of the pit are lined with sheetrock panels and a liquefied fiberglass mixture is sprayed onto the panels and the concrete slab. One or more underground storage vessels are then placed within the vault, secured to the floor by conventional anchors and cables and connected to conventional supply lines. The anchors may be placed in the concrete base prior to its hardening or may be placed in a base layer of pea gravel contained within the vault. Once the vessels are anchored, the remainder of the vault is backfilled with further pea gravel.
One example of a vault which is pre-fabricated and assembled on-site is provided by U.S. Pat. No. 4,961,293 issued Oct. 9, 1990 to House et. al. This patent describes a precast, prestressed concrete secondary containment vault comprised of a number of units including a bottom unit, a top unit and a collar or side unit. Each unit is comprised of one or more concrete panels which interlock to form the various units of the vault. Cradles for supporting the storage vessels are contained within the bottom unit. To install the vault, the construction location is first excavated and a sand bed is graded. The bottom unit is then lowered into the excavation pit and leveled. The cradles are pinned to the inner face of the bottom unit. The collar unit is then lowered onto the bottom unit and the storage vessel is installed therein. Finally, the top unit is lowered into place and the excavation pit is backfilled.
Further, U.S. Pat. No. 5,037,239 issued Aug. 6, 1991 to Olsen et. al. describes a vault structure designed so that all of the panels used in its construction may be precast at a remote site and transported to the construction site for assembly. The construction site is excavated and prepared for the structure. The floor panels are then lowered into the excavation and assembled, followed by positioning of the walls, storage vessels and roof. The storage vessels are supported on the floor by cradles. More particularly, the vault is comprised of three precast concrete floor panels, three precast concrete roof panels and four precast concrete wall panels. The size and number of the panels is limited by the allowable size and weight of panel that can be transported to the construction site.
U.S. Pat. No. 5,664,696 issued Sep. 9, 1997 to Canga describes a two stage construction of an underground vault. The first stage is a lower stage which includes a floor and part of the sides extending up to a level approximately that of the height of the storage vessel. The second stage is an upper stage which rests on the lower stage and which supports the lid of the vault. Once the lower stage is lowered into place in the excavation, a bed of filler material is poured into the lower stage. The storage vessel is placed within the lower stage on the bed of filler material. Once the piping to the surface is connected, further filler material is added and the upper stage is lowered into position. The lid is then placed on the upper stage. The walls of the vault have means for coupling slings for hoisting and lowering the vault. These coupling means may also be used for attaching deadweights after installation, in place of a more conventional anchoring system. The deadweights are required to stabilize the vault underground and to avoid flotation which may endanger the vault structure and the fittings or piping.
Further examples of pre-cast or pre-fabricated vaults are provided by U.S. Pat. No. 5,391,019 issued Feb. 21, 1995 to Morgan and U.S. Pat. No. 5,495,695 issued Mar. 5, 1996 to Elliot. Jr.
Thus, there remains a need in the industry for an improved submersible storage vessel system. Further, there is a need for a submersible storage vessel system which may be transported to and installed at the construction site as an integral unit. As well, there is a need for an integral unit or system which supports the storage vessel with respect to the downward gravitational forces applied to the storage vessel and which supports or anchors the storage vessel against any upward buoyancy forces applied to the storage vessel. Further, the integral unit or system preferably protects the storage vessel during installation and transportation to the site and aids in the installation of the storage vessel. Finally, there is a need for an integral unit or system which provides support to the fittings or piping connected to the storage vessel, particularly at the location of the connection of the fitting to the vessel.